Browsing by Author "Lerch, Jean Oliver"
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- ItemInvestigation into the Effect of Fibre Geometry on the Performance of Macro Synthetic Fibre Reinforced Concrete(Stellenbosch : Stellenbosch University, 2016-03) Lerch, Jean Oliver; Boshoff, William Peter; Van Rooyen, Algurnon Steve; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Unreinforced concrete has the inherent shortcomings of low tensile strength and low strain capacity at fracture (ACI Committee 544, 2002). In order to overcome these shortcomings, fibres can be added to the fresh concrete with the aim to introduce ductility to the brittle concrete matrix. Synthetic fibre reinforced concrete (FRC) gained popularity over the past years (Bolat et al., 2014), finding its primary application in ground supported slabs. The purpose of this research is to improve the general understanding of macro synthetic FRC on the single-fibre and the macro-mechanical level. Special attention is given to fibres with various geometric properties such as fibre length, profile and fibre shape. Single-fibre pull-out (SFPO) experiments have been conducted on macro synthetic fibres with various embedment lengths. Fibres were premixed prior to embedment into the fresh concrete paste matrix to investigate in-service conditions. The effect of premixing was especially noted for flat fibres, indicating an increase in interfacial bond exceeding 100 % in contrast to virgin unmixed fibres, depending on the embedment length. Embossed fibre profiling proved to be the most efficient fibre geometry, providing the highest interfacial bond with the surrounding paste matrix. It is generally accepted that a high interfacial bond is a good indication for the overall performance required in typical macro synthetic FRC applications. Additionally, time dependent pull-out (TDPO) experiments have been conducted on single embedded fibres. It was found that premixing has a significant influence on the TDPO performance, withstanding sustained loads considerably longer than unmixed fibres. Embossed fibre geometries revealed substantial resistance against sustained loads, undergoing very little displacement, being representative for small time dependent crack openings in contrast to non-embossed fibre geometries. Non-embossed fibre geometries typically exhibited considerable pull-out displacement, demonstrative for large crack openings. Small time dependent crack opening is a property desired when structural soundness is required. Macro-mechanical tests were performed in order to establish parameters required in the structural design aspect of synthetic FRC, as these type of tests represent the in-service conditions of macro synthetic FRC. It was found that the embossed fibre profile indicated the highest performance followed by that of the flat fibre type. Robust macro-mechanical performance is required for the development of economic macro synthetic FRC elements and a reduced eco-footprint. In addition, macro-mechanical experiments have been conducted on macro synthetic FRC subjected to prolonged mixing times. It has been established that prolonged mixing typically decreases the post-cracking performance of macro synthetic FRC. Therefore, mixing time has a significant influence on the structural performance of macro synthetic FRC. It has been recognised that the best overall structural performance is achieved by embossed fibre geometries. In addition, the mixing stage was found to have a significant influence on the fibre performance in the hardened state, especially for flat fibres. Depending on the type of macro synthetic FRC application, longer fibre lengths are required for higher levels of deformation, while shorter fibre lengths revealed adequate performance for lower levels of deformation. Furthermore, TDPO experiments revealed concerning behaviour of nonembossed polypropylene macro synthetic fibres.